1. Field of Invention
Aspects of the invention can relate to a prism structure used in a projector and a projector.
2. Description of Related Art
FIG. 8 is a diagram of a related art optical system for a projector. In the drawing and the following description, the z-axis represents an axis along the direction of travel of light (the optical axis formed by a series of optical elements constituting an optical system). The x-axis and the y-axis represent axes that are normal to the z-axis and perpendicular to each other. As shown in FIG. 8, a projector 90 separates the light emitted from a light source 110 into three colors of light, red, green, and blue, by a color-separating optical system 200, modulates the respective colors of light by three electro-optic devices 310R, 310G, and 310B, combines them with a color combining prism 400, and projects the composite light onto a screen S, or the like, through a projector lens 420. Such related art projectors 90 widely use a prism structure 500 that is a combination of part of the components of the electro-optic devices 310R, 310G, and 310B and the color combining prism 400.
FIG. 9 is a perspective view of a related art prism structure 500, and FIG. 10 is an exploded perspective view of the related art prism structure 500. As shown in FIGS. 9 and 10, the prism structure 500 has an integrated structure in which parts of the components of the three electro-optic devices 310R, 310G, and 310B are attached to three sides of the quadratic color combining prism 400. The emerging plane of the color combining prism 400 which has not the electro-optic devices 310R, 310G, and 310B, in the rear of the drawing, is opposed to the projector lens 420.
While FIG. 10 shows the component of only the electro-optic device 310G as being exploded, the other electro-optic devices 310B and 310R have the same structure. The electro-optic device 310G can include an incident-side polarizing plate (arranged on the side of the incident light of a liquid crystal panel 311, not shown), the liquid crystal panel 311, a view-angle compensating plate 320, a fixing plate 330, and an emerging-side polarizing plate 340. Among the components, the components other than the incident-side polarizing plate are integrated with the color combining prism 400. A rectangular frame 312 that holds the liquid crystal panel 311 has pin holes 313 for transparent pins 350 to pass through at the four corners.
The fixing plate 330 is a rectangular member formed of, for example, a metal plate having a thickness of about 0.7 mm. The fixing plate 330 has an opening 331 for image light that has passed through the liquid crystal panel to pass through and a recess 332 for mounting the rectangular emerging-side polarizing plate 340 and the view-angle compensating plate 320. The fixing plate 330 also has two positioning guide holes 333 bored at the lower part.
The projector 90 can be used as a so-called data projector for projecting the screen of a personal computer onto a screen or the like at a meeting, a discussion and so on. The data projector can project high-intensity light so as to allow clear projection display even in a bright room. On the other hand, also widely used as so-called home-theater projectors which project the screen of movies and music lives onto a screen or the like at home or mini theaters. The home-theater projectors generally make projection display in a dark room.
However, when the so-called data projectors used in a bright room is used in a dark room, various problems are caused. One of them is the presence of stray light that leaks around the projection image. Although the stray light leaking around the projection image is not conspicuous when the projector is used in a bright room, it becomes conspicuous to be extremely obstructive when it is used in a dark room.